The invention relates to crystalline gallium nitride. In particular, the invention relates to a homoepitaxial gallium nitride based photodetector and a method of producing the same.
During the past decade there has been tremendous interest in gallium nitride (GaN) based optoelectronic devices, including, for example, light emitting diodes (LEDs) and laser diodes (LDs). Because high-quality GaN substrates have not been available, virtually all of the art has involved heteroepitaxial deposition of GaN and GaInAlN on sapphire or SiC substrates. A thin low-temperature buffer layer, typically AlN or GaN, is used in order to accommodate the lattice mismatch between GaN and the substrate and maintain an epitaxial relationship to the substrate.
Several processes are currently used to produce crystalline gallium nitride substrates. The processes include heteroepitaxial growth of gallium nitride on a substrate, such as a sapphire or silicon carbide. The heteroepitaxial growth process often results in defects including high concentrations of dislocations, vacancies, or impurities. These defects may have undesirable and detrimental effects on epitaxially grown gallium nitride, and may adversely influence operation of the resultant gallium nitride-based device. These adverse influences include compromised electronic performance and operation. Presently, heteroepitaxial gallium nitride growth processes require complex and tedious steps to reduce defect concentrations in the gallium nitride.
Known growth processes do not provide large gallium nitride crystals of high quality (i.e.; crystals having low dislocation densities); for example, gallium nitride crystals greater than about 0.8 inches (about 2 centimeters) in diameter or greater than about 0.01 inches (about 250 microns) in thickness. Further, the known methods are not known to provide for production of large gallium nitride crystals that result in single-crystal gallium nitride boules, for example gallium nitride crystals of about 1 inch in diameter and about 0.5 inches in thickness, which are suitable for forming wafers. Thus, applications for gallium nitride are limited due to size constraints.
Known methods of producing large-area GaN wafers yield wafers having rather high (>106 cm−2) concentrations of threading dislocations. As is the case in heteroepitaxial devices, high concentrations of such defects degrade device performance.
Also, most known gallium nitride crystal production processes do not provide high-quality gallium nitride crystals with low concentrations of impurities and dislocations with adequate size and growth rates that are acceptable for device applications. Further, the known gallium nitride crystal production processes are not believed to provide an economical process having nitride growth rates that enable moderate-cost gallium nitride crystal production. Therefore, applications for gallium nitride are further limited due to quality and cost-of-production factors.
Use of gallium nitride crystal has been limited in photodetector applications because of the quality and manufacturing issues discussed above. A high-performance photodetector could be used, for example, to control the temperature in the combustor of power-generation turbines or in aircraft engines, allowing continuous, real-time optimization of combustion conditions and improved energy efficiency and reliability. Photodetectors could also be used in a wide variety of sensor applications, both civilian and military. While current buffer-layer technology allows for production of commercially viable GaN-based LEDs and LDs, the photodetectors that can be produced with current technology are marginal in performance because of very high defect levels.
Growth of homoepitaxial photodetectors on high-quality GaN substrates would offer improved sensitivity, increased efficiency, reduced leakage (dark) current, and increased breakdown field. Other potential benefits of homoepitaxial photodetectors include increased temperature of operation, better reliability, better device uniformity, improved backside contact capability, higher manufacturing yield, longer lifetime, enhanced wafer utilization, improved wavelength selectivity, and better manufacturability.
Accordingly, there is a need in the art for an improved GaN based photodetector.